This invention relates to microwave frequency gain-equalizers, and more particularly to a monolithic microwave integrated circuit (MMIC) variable slope gain-equalizer incorporated into a microstrip transmission line system.
The use of a microstripline waveguide formed as part of an MMIC in a microwave system that includes a microwave amplifier is known in the art. The nominal gain versus frequency characteristic of such an amplifier in a microwave system generally has a component that is independent of frequency but temperature dependent, and a component that is both temperature and frequency dependent. Typically the slope of the gain versus-frequency temperature dependent characteristic (the "gain slope") of such an amplifier becomes more positive with decreasing temperature, and more negative with increasing temperature.
It is known in the art to use an attenuator that is frequency independent to compensate for the gain versus frequency temperature changes that are frequency independent. However such an attenuator does not compensate for an amplifier's frequency dependent gain changes over temperature. It is desirable, therefor, to compensate for temperature dependent gain slope changes by inserting a circuit following the amplifier to equalize the gain-versus-frequency temperature characteristics of the amplifier. In a system capable of about 0 to 30 dB gain, such a circuit should exhibit a variable slope gain-versus-frequency transfer function, preferably over a range of about -0.6 dB/GHz to about +0.2 dB/GHz. Linearity should be within about 0.5 dB over a DC to 18 GHz range, and the voltage standing wave ratio (VSWR) at the input and output ports of the circuit should be 2:1 or less.
Applicant is not aware of any circuits exhibiting such characteristics in the prior art.